1. Technical Field
The subject matter of the present invention relates to an improved method and system for measuring material properties of laminated circuit boards, and in particular to non-destructive ultrasonic measurement techniques. More particularly, the present invention relates to combining an ultrasonic circuit board material analysis with a cepstrum noise filtration process, thereby providing an accurate and efficient method and system for obtaining a material property profile for an anisotropic circuit board.
2. Description of the Related Art
Ultrasonic measurement techniques are sometimes utilized as a non-destructive alternative to traditional destructive material properties testing techniques. In order to evaluate the composition of an anisotropic circuit board in terms of its structural and chemical properties, it is necessary to analyze the material composition of the circuit board at various stages during circuit board fabrication. A test sample of the fabricated circuit board may be removed and subject to various testing procedures such as ASTM tensile tests. Such testing is economically inefficient both in terms of loss of usable circuit board material and in terms of the time consuming nature of such a two-step testing procedure.
One alternative to destructive circuit board testing techniques, are non-destructive material property characterizations performed utilizing ultrasonic waves. Such ultrasonic testing techniques are capable of characterizing the ultrasonic wave medium being observed. In the case of anisotropic circuit boards, this medium is composed of more than one element or material utilized as the supporting structure on which integrated circuit (IC) devices and modules are physically and electrically arranged and interconnected. Ultrasonic waves are induced into a test medium and observation of the composition of the test medium is accomplished utilizing ultrasonic waves reflection within the test medium.
The attenuation characteristic of reflected ultrasonic waves is often utilized as the parameter for discriminating among a layered isotropic material composition. As explained by Shimura et al. in U.S. Pat. No. 4,655,228, such an analysis relies on the fact that when an ultrasonic wave travels a distance, dz, over a given time interval (referred to hereinafter as xe2x80x9ctime-of-flightxe2x80x9d), the sound pressure is attenuated in accordance with the following relation:
EXP{xe2x88x92xcex1(z,f)dz},
wherein xcex1(z,f) varies as a function of location, z, and frequency, f.
However, due to the complexity involved in translating ultrasonic wave reflection within an anisotropic material, conventional ultrasonic material measurement procedures have suffered from problems associated with inadequate noise filtration.
It can therefore be appreciated that a need exists for a non-destructive method and system for obtaining a material property profile for an anisotropic circuit board, such that a reliably accurate and noise-free profile of material composition may be obtained.
It is therefore an object of the invention to provide an improved method and system for measuring material properties of laminated circuit boards, and in particular to non-destructive ultrasonic measurement techniques.
It is another object of the invention to provide a method and system for combining an ultrasonic circuit board material analysis with a cepstrum noise filtration process, thereby providing a accurate and efficient method and system for obtaining a material property profile for an anisotropic circuit board.
The above and other objects are achieved as is now described. A method and system for determining material properties of a cross-section of an anisotropic sample material are disclosed. An ultrasonic signal is applied to the surface of the anisotropic sample material, which comprises multiple constituent material layers, such that a characteristic medium wave is induced within each of the constituent materials. Each of these characteristic medium waves is sampled over a time interval to obtain a test waveform. This resultant test waveform is then spectrum analyzed utilizing cepstrum noise filtration, such that the material properties of said anisotropic sample material may be determined.